None exec_jwst_tweakreg_miri_test

JWST Pipeline Validation Testing Notebook: Calwebb_Image3, Tweakreg step with MIRI imaging

**Instruments Affected**: FGS, MIRI, NIRCam, NIRISS

Tested on MIRI Simulated data

Table of Contents


[Introduction](#intro_ID)
[Run JWST Pipelines](#pipeline_ID)
[Imports](#imports_ID)
[Create an association table for your cal files and run them through calwebb_image3](#runpipeline_ID)
[Find Stars in Image and Determine their Coordinates](#runscript_ID)
[Compare RA and Dec to expected Values](#residual_ID)
[About This Notebook](#about_ID)

Introduction

This test is designed to test the tweakreg step in the calwebb_image3 pipeline. At the start of the calwebb_image3 pipeline, the shifts between the images in an association table are found. This step creates image catalogs of point-like sources whose centroids are then used to compute corrections to the WCS of the input images such that sky catalogs obtained from the image catalogs using the corrected WCS will align on the sky.

For more information on the pipeline step visit the links below.

Step description: https://jwst-pipeline.readthedocs.io/en/latest/jwst/tweakreg/README.html

Pipeline code: https://github.com/spacetelescope/jwst/tree/master/jwst/tweakreg

The data for this test were created with the MIRI Data Simulator, and the documentation for that code can be found here: http://miri.ster.kuleuven.be/bin/view/Public/MIRISim_Public

Calibration WG Requested Algorithm:

A short description and link to the page: https://outerspace.stsci.edu/display/JWSTCC/Vanilla+Refine+WCS

Defining Terms

Definition of terms or acronymns.

JWST: James Webb Space Telescope

MIRI: Mid-Infrared Instrument

MIRISim: MIRI Data Simulator

Description of test

This test is performed by creating a set of simulated data with multiple point sources located at specified coordinates. The simulator puts in the expected distortion, so the initial output data comes out of the simulator in distorted coordinates. When this data is then run through calwebb_detector1, calwebb_image2 and calwebbb_image3, the combined, undistorted image should have the point sources registered at the expected locations. In flight, this test can be repeated with known stars that should be found at their expected coordinates. If there is a shift in coordinates between the images that was not expected, tweakreg will find the sources to create a better image alignment. This is checked by using DAOStarFinder to find the point sources in each image (individual and combined) so that the catalogs can be compared to the expected RA and Dec values that were used to create the images. The user will look at whether the statistics of the combined sources are better or worse than those of the individual images.

Description of data

The data used in this simulation were created with the MIRISim simulator.

The simulation consists of eight files, two exposures each at four different dither positions. The images used in this test have 50 bright point sources scattered across the images, and were created in the F1130W filter.

Top of Page

Create a temporary directory to work in and read in data

Run the calwebb_detector1 pipeline to get rate.fits files.

Run calwebb_image2 pipeline to create cal.fits files

Test # 1: See what happens with tweakreg when given data with no shifts.

This test uses MIRISim data using only the simulated dithers, and no shifts. Two exposures each of four different dithers, perfect alignment.

First look at the cal images out of calwebb_image2.

Run the images through calwebb_image3 with tweakreg on

Alter any parameters needed to get better results from tweakreg. Look at individual i2d images afterwards.

Go through list of individual images and see which sources were found for each image.

Get position differences as found earlier for the individual i2d files

Look at positions of RA, Dec and get stats on differences for the combined image run with tweakreg on

Run calwebb_image3 with tweakreg turned off

Re-run the pipeline with tweakreg turned off to see if the differences found in the previous step are due to tweakreg alone, or differences in the distortion model that would show up in any run of the calwebb_image3 pipeline.

Test # 2: See what happens with tweakreg when there are shifts between images not tracked in the wcs.

This test uses MIRISim data using only the simulated dithers, and one shifted image. Two exposures each of four different dithers.

First look at the cal images out of calwebb_image2.

Run the images through calwebb_image3 with tweakreg on

Alter any parameters needed to get better results from tweakreg. Look at individual i2d images afterwards.

Go through list of individual images and see which sources were found for each image.

Look at positions of RA, Dec and get stats on differences for the combined image run with tweakreg on

Test again with tweakreg off

Criteria for success.

If the first set of images with no shift are well aligned as shown in images and the statistical comparison, that test passes.

Once a shift is added, the statistics and number of sources found don't tell the whole story. Look at the combined images shown after image3 with and without tweakreg. If the image run with tweakreg shows double sources just like the image without tweakreg, then the test fails. If the image doesn't show double sources and looks like the unshifted combined image, then the test passes. Examine the image to look for obvious faults like stars that were not identified as stars, those with multiple star identifications, double star images, etc.

About this Notebook

Authors: M. Cracraft, M. Libralato and K. Gordon, MIRI Branch

Updated On: 08/25/2021